The present invention relates to an optical amplifying device for amplification of an optical signal incident towards a photo diode comprising a laser device and an electrical feeding circuit. The invention also relates to the use of such devices. Optical amplifying devices are used among others in optical transmission technology such as in optical transmission systems etc for amplification of optical signals. Among others they are used as repeater elements for regeneration of optical signals, for example within telecommunications etc. Such devices are however often complicated since amplifying electronics is required and therefore also noise may strongly influence the device. Furthermore often a considerable number of separate components are required which may result in the device being complicated and sensitive.
A number of different amplifying devices are known, for example laser amplifiers, among others semi-conductor amplifiers and erbium doped fibre amplifiers. These known devices however require advanced electronic equipments which as such make the devices complicated. Therefore the noise level often gets high. Furthermore a larger number of separate or non-integral components are required which among others make such devices expensive.
In "Low Noise Opto Electronic Amplifier using Sub Shot Noise Light" of P. J. Edwards in Electronics Letters 4th Feb. 1993, Vol 29, No. 3, a low noise opto electronic amplifier is described. This device is illustrated schematically in FIG. 1 and it comprises a number of (in the shown embodiment 4) diode lasers or light diodes (LEDs) connected in series. In this case four separate lasers are interconnected. When an optical signal is incident towards a photo diode four, as far as the output power is concerned, essentially exact replicas of the input signal are obtained. These replica or output signals are however optically incoherent which often leads to a number of limitations for the device practically as well as economically.